1. Field of the Invention
The present invention relates to a fuel reforming apparatus that simultaneously achieves a steam reforming reaction to produce hydrogen from a hydrocarbon and steam and a partial oxidation reaction to produce hydrogen from a hydrocarbon and an oxidizer and uses heat generated by the partial oxidation reaction that is an exothermic reaction to cover heat for the steam reforming reaction that is an endothermic reaction.
2. Description of the Related Art
An example of a methanol reforming apparatus for a fuel cell is disclosed in Japanese Unexamined Patent Publication No. 11-092102. An object of this apparatus is to spatially equalize a temperature distribution in a fuel cell reforming apparatus. The sixth and seventh embodiments of the disclosure temporally change an oxidizer feeding position with respect to a catalyst, to prevent a local temperature increase in the catalyst due to a continuous localized oxidation reaction, promote an internal oxidation reaction, and shorten a startup time.
This prior art intentionally prevents a localized oxidation reaction, which is an exothermic reaction, and spatially disperses heat produced by the oxidation reaction. Accordingly, the prior art needs a large amount of fuel and time to increase the temperature of a catalyst to an activation level, and therefore, is incapable of shortening a startup time.
If a part of a catalyst is heated to an activation temperature on startup, the surface of the catalyst starts a chemical reaction to generate heat, which causes a chain reaction of heating the periphery of the heated part of the catalyst, thereby promoting reactions. Therefore, to shorten a startup time, it is necessary to quickly heat, even locally, a catalyst to an activation temperature. The prior art, however, pays no attention to this point.
An object of the present invention is to provide a fuel reforming apparatus capable of quickly heating a catalyst to an activation temperature and shortening a startup time.
In order to accomplish the object, a first aspect of the present invention provides a fuel reforming apparatus that supplies, on startup, a hydrocarbon fuel and an oxidizer upstream from a second catalyst and supplies steam upstream from a first catalyst. As a result, the second catalyst starts a rapid oxidation reaction to produce a high-temperature gas, which quickly heats the first catalyst that is downstream of the second catalyst. At the same time, carbon monoxide (CO) produced on the second catalyst reaches the first catalyst and reacts (a shift reaction which is an exothermic reaction) with steam on the first catalyst to promote the heating of the first catalyst. At this time, carbon monoxide produced on the second catalyst is purified into carbon dioxide through a shift reaction on the first catalyst.
To change the startup operation (or an accelerating operation) to a steady operation after a predetermined period, the apparatus supplies the hydrocarbon fuel and steam upstream from the second catalyst and supplies the oxidizer upstream from the first catalyst. As a result, a steam reforming reaction, which is an endothermic reaction, occurs on the second catalyst, to rapidly cool the second catalyst and stop reactions on the second catalyst. The hydrocarbon fuel and steam passed through the second catalyst without reactions cause a partial oxidation reaction and steam reforming reaction on the first catalyst that is downstream of the second catalyst, to generate a hydrogen-rich reformed gas.
With these processes, the fuel reforming apparatus of the first aspect shortens a startup time, minimizes the poisoning of a fuel cell arranged downstream of the fuel reforming apparatus, and suppresses the generation of by-products that may deteriorate the quality of emissions.
A second aspect of the present invention uses a temperature measured around the first catalyst as a parameter to determine whether or not a startup operation or an accelerating operation must be changed to a steady operation. This smoothly changes a startup operation or an accelerating operation to a steady operation while suppressing the generation of by-products.
A third aspect of the present invention employs an integrated material feeder for each of the first and second catalysts, to feed an oxidizer and steam to the catalysts. This aspect simplifies the structure of the fuel reforming apparatus.
A fourth aspect of the present invention applies the fuel reforming apparatus of the present invention to a fuel cell system using methanol as a fuel.
A fifth aspect of the present invention employs an oxidation catalyst, which is commonly available, to improve the durability of the fuel reforming apparatus and reduce the cost thereof.